Boring a super smooth surface

Do you mean "bearing smooth"?

"CAMCOMPCO" wrote in news: snipped-for-privacy@g44g2000cwa.googlegroups.com:

A burnishing tool is the usual way. Barring that, if it's a through hole you can "ballize" the hole. In other words, drill and ream the hole slightly undersize then press the appropriate size ball bearing ball through the hole. You can also use emory wrapped on a wooden dowel to polish the I.D. (put a slot on the end to help with the wrap) and then follow up with a split lap and some lapping compund.

Yes, bearing, 7 years of University studies never taught me to second guess spell check ;-)

This is as a general skill question...I want the hole to be exactly XYZ when I am done, in practice, +/- 0.001. Now, I can get the hole that precise, just cant get it glass smooth. If I am to understand the ballize description provided by Dan, the hardened ball bearing is pushed through the hole, essentially smashing the bumps and scratched flat. Now I have a reason to hunt for ball bearings on ebay.

I'll try the emery wrap, just don't want to sand away accuracy....I give it a try tomorrow provide update...

Cheers, and thanks again Larry and Dan

John

Yes, bearing, 7 years of University studies never taught me to second guess spell check ;-)

This is as a general skill question...I want the hole to be exactly XYZ when I am done, in practice, +/- 0.001. Now, I can get the hole that precise, just cant get it glass smooth. If I am to understand the ballize description provided by Dan, the hardened ball bearing is pushed through the hole, essentially smashing the bumps and scratched flat. Now I have a reason to hunt for ball bearings on ebay.

I'll try the emery wrap, just don't want to sand away accuracy....I give it a try tomorrow provide update...

Cheers, and thanks again Larry and Dan

John

"CAMCOMPCO" wrote in news: snipped-for-privacy@o13g2000cwo.googlegroups.com:

Exactly right. Kind of a poor man's burnishing tool. Here's a guy on Ebay that sells gage balls (cheap):

Nice find! But where are his metric-sized gage balls? :(

- Michael

Just what I was looking for...thanks a bunch

John

Last weekend I made an eccentric strap, similar to a connecting rod, for a small steam engine. The eccentric strap (follower) needed to fit the eccentric loosely enough to turn with usu. oil film. First, the strap was made to outside dimensions with the bolt holes drilled and tapped - flats were left on 2 sides perpendicular to the split lines, which is the normal profile for an eccentric strap. Then the rough opening was bored to within a few thousandths of finished size which was to be 0.806". Next, I made a pair of go-no-go gauges on the lathe, of 0.806" and 0.808". (Wish I had a set of gauge rods or balls) The strap was repositioned in the mill with the flats oriented for splitting. It was split with a 0.020" slitting saw through each side and the sides tightly bolted together. Next, it was recentered in the mill and bored to near 0.806". Several boring passes were made until the 0.806" gauge would just barely "go". The 0.808" gauge would not "go". That yielded a very round hole (after splitting) of very nearly

0.806", maybe 1/2 to 1 thousandth over, but certainly between 0.806" and 0.808". Measuring with test gauges is a lot less "nervous" than the usu. small hole gauges, at least for me. One thing to note: When very nearly to finished size, 1 or 2 tenths can be removed by running the boring tool down into the hole again, maybe more than once.

The first thing is to bore the hole properly. You can get smooth surfaces on the outside of a turning, you can do the same for the inside of a bore with the right geometry on the cutting tip. After that, the ball or a rod with a large end will definietely roll over the sharp edges but will also make the scrapes along the radius of the bore rather than around the bore. This may be more harmful than leaving a slightly rougher surface around the bore. Better would be to hone with either honing cutters or stones to keep the right orientation of the grooves that are left and get the right size for the hole. If you're making a split bearing surface, don't forget to use Plastigage on the bearing to make sure that it is the right clearance that you desire. The Plastigage is available at any auto machine shop or better auto parts store. Once you have used the stuff on a bearing and see how well it works, you'll never go back to any othe method of checking bearing clearances.

-- Why do penguins walk so far to get to their nesting grounds?

Right on, Bob! I totally agree; it is unwise to force anything through a finished hole. Doing so, may bring the hole "to size", but it will surely leave minute damage of its own. Thanks for the tip on Plastigage. I will check on it.

So is this a vote for not "ballizing" the hole with a bearing.....Dan, what say you. Have you had success with it? It's interesting to note how opinions on certain topics can generate both support and condemnation at the same time...

Thoughts and comments from others...I guess I am going to cram a ball in the hole, cut the "tube" open and check with a microscope myself....Once I get my ball bearings in, I'll check and get back to you all with the findings.

By the way, I never commented on the material....mostly CRS, SS or Aluminum (mostly fortal these days).

Thanks again all.

John

John, You will find that gummier metals, like crs, will give you a better finish than harder materials. Be sure to use the correct lube. Cheers, Eric R Snow, E T Precision Machine

SNIP

Hey Eric and John,

Owwwwww...gotta diagree with THAT Eric. The harder the metal, the better the surface will get, if done properly. Mirror, and I mean MIRROR finishes in say D-2 are done by "hand men", whose job it is to polish (and keep with-in size) the suface left by mill or lathe. They start off with what-ever is rerquired in nthe 40 to 80 grit range, and finsih with diamond paste, usally with a Foredom or Dumore hand-piece.

Take care.

Brian Lawson, Bothwell, Ontario.

I could be wrong Brian, but, I think Eric may have been referring to the Ballizing part from above, Correct me if I am wrong Eric. Now, given that, Brian, you might still be absolutely correct :-)

Cheers

Ballsizing is a fairly common commercial method of sizing and finishing holes. Should be lots of references to in on the web.

Dan

Brian, I meant that gummier materials will look better with ballsizing than hard materials. My experience with ballsizing and roller burnishing is limited, but that's the way it always worked for me, and was what I was told would happen. Like form tapping. gummier, to a point, is better, Of course, harder materials will polish up better. Eric

"DeepDiver" wrote in news:FdOZe.298$ snipped-for-privacy@typhoon.sonic.net:

Don't know, but he must have bought a dump truck full of "inch" sized ones at an auction or something. He's been selling them on ebay for some time now.

"CAMCOMPCO" wrote in news: snipped-for-privacy@g47g2000cwa.googlegroups.com:

It's a crude form of burnishing. Thousands upon thousands of parts are burnished everyday. This type of thing would be a big no-no in a medical implant where impurities can get "rolled in", or in a critical application where surface integrity was important, say in a tool steel that was to be heat treated later. On materials that work harden it may raise the hardness slightly. In all likelyhood the Aluminum might not work as well as the stainless or CRS.

The trick is to get the hole straight, to the right size, and finish to start with. That might take a little experimentation.

As far as burnishing a bearing surface, It's done all of the time. It's how .0001" diameter tolerances are held on Swiss screw machine on the tiny shafts inside clocks and watches. It's also how many manufacturers of power tools size the shafts that run in race bearings.

The downside to using a ball is that it will happily follow a crooked hole, and a big high spot in the hole will tend to push the ball over to the lower side.

Cheaper, and metric sizes as well, from McMaster-Carr.

Ned Simmons